#include <iostream>

class A{
    public:
    virtual void foo() = 0;
};

void A::foo() { std::cout << "A foo"; }

class B : public A{};

class C : public A{
    public:
    void foo();
};

void C::foo() { std::cout << "C foo"; }

class D: public A{
    public:
    void foo();
};

void D::foo() { A::foo(); }

class E: public A{
    public:
    //using A::foo;
    void foo(int) { std::cout << "E foo"; }
};

int main(){
    (new A)->foo();  // 1
    (new B)->foo();  // 2
    (new C)->foo();  // 3
    (new D)->foo();  // 4
    (new E)->foo(2); // 5
}